This invention relates to the removal of water from a hydrogel. In one of its aspects this invention relates to the production of dried porous structures suitable for catalyst support. In another of its aspects this invention relates to a polymerization with chromium-containing catalysts supported on a substrate prepared from a hydrogel. In yet another of its aspects this invention relates to the production of ethylene polymers having a melt index in excess of about 6.6.
The preparation of chromium-containing polymerization catalysts supported on substrates prepared from hydrogels is well known. The preparation of hydrogels and removal of water therefrom to produce these substrates has been described in a variety of methods. The impregnation of polymerization catalysts onto supporting substrates is also well known. Up to this time, however, the methods for producing a chromium-containing catalyst impregnated upon a support for polymerization of ethylene polymers has not shown means by which a melt index of at least 6.6 can be obtained.
In U.S. Pat. No. 3,890,249 a method of producing a xerogel which is used as catalyst support in ethylene polymerization is set out in which large pore support is produced by dehydration of the hydrogel using any solvent in which water is partly soluble as a dehydration treatment agent. We have discovered that the solvent used in such a treatment of the hydrogel support to remove water therefrom can clearly affect the melt index of the polymer produced in polymerization reactions using a catalyst supported on strata produced from the hydrogel.
It is an object of this invention to provide a method for removing water from a hydrogel which will provide retention of porous structure in the dried product. It is another object of this invention to provide a substrate suitable as a catalyst support. It is yet another object of this invention to provide a supported chromium-containing catalyst suitable for producing polymers of ethylene having melt index in excess of 6.6.
Other aspects, objects and the various advantages of this invention will become apparent upon reading the disclosure of this specification and appended claims.